1. Field of the Invention
An energy absorbing member for shock absorbing steering column apparatus according to the present invention is connected between a steering column and a car body, thus constructing a shock absorbing steering column apparatus. The shock absorbing steering column apparatus is designed to protect the passenger's life upon crash by displacing the steering column ahead while absorbing shock and relieving impact exerted on the passenger's body upon crash.
2. Related Background Art
In a car crash, following a so-called primary collision, where a car collides with an object, such as another car, a so-called secondary collision, where a driver collides with a steering wheel, will occur. In order to lower the impact exerted on the driver upon the secondary collision so as to protect the driver's life, it is conventional that the steering shaft with a steering wheel fixed at one end thereof is constructed as a so-called collapsible steering shaft, the total length of which is decreased with application of strong impact thereon, and the steering column through which the steering shaft is inserted is constructed as a shock absorbing type.
A conventional example of the steering column apparatus of the shock absorbing type used for such a purpose is one disclosed in Japanese Laid-open Utility Model Application No. 63-76578. FIGS. 9 to 12 show the shock-absorbing steering column apparatus as described in the application. As shown in FIG. 9, a steering shaft 1 has a steering wheel 2 fixed to a rear end (right upper end in FIG. 9) thereof and is arranged to rotate through manipulation of the steering wheel 2. The steering shaft 1 is so arranged that the total length thereof contracts with application of axial impact via a telescopic mechanism, (not shown), for example, a spline engagement. A tubular steering column 3 with the steering shaft 1 inserted therein is fixed to portions of body 4, e.g., to a lower surface of dash board, so as to be supported at an intermediate portion and a lower end portion. Namely, the lower end of steering column 3 is supported by a lower support bracket 5 fixed to a part of body 4 so as to be slidable along the axial direction.
On the other hand, an upper support bracket 6 formed by bending a metal plate is fixed, for example, by welding, to the outer periphery of the intermediate portion of the steering column 3. A pair of mount plate portions 7 are formed on either side of the upper support bracket 6 for securing the upper support bracket 6 to the body 4. A U-shaped cut 8 is formed in each mount plate portion 7 so as to be open on one edge (an edge on the steering wheel 2 side) of each mount plate portion 7. A stop member 9 formed in a long C shape of an aluminum alloy, a synthetic resin, or another material is externally fit over one edge of each mount plate portion 7 so as to cover the cut 8. Then a bolt 10 is inserted through a through hole 15 formed in the stop member 9, and through the cut 8 to mate with a thread hold provided on the body 4. Upon tightening this bolt 10, the stop member 9 strongly pinches the mount plate portion 7, whereby the upper support bracket 6 is supported through the stop member 9 by the body 4. In addition to the above arrangement where the bolt 10 is engaged with the thread hole provided on the body side, there are cases where a nut is brought into engagement with a bolt fixed to the car body.
Further, one end of energy absorbing member 11 is welded to each mount plate portion 7. A through hole is formed at the other end of energy absorbing member 11 and the bolt 10 is also set through this through hole 16. Each energy absorbing member 11 is made of a plastically deformable belt plate, for example, a metal plate of mild steel, and has a U-shape folded portion 12 in a middle portion. This folded portion 12 is pinched between the mount plate portion 7 and a guide plate 13 as next described, from above and below. Each guide plate 13 formed by pressing a metal plate is secured by welding to either side surface of the upper support bracket 6 below the mount plate portion 7, so that a guide space 14 for guiding the folded portion 12 of the energy absorbing member 11 is formed between the upper surface of each guide plate 13 and the lower surface of each mount plate portion 7.
The first conventional example of the shock absorbing steering column apparatus is designed to assure the safety of driver's life in a crash, by operating in the following manner. When impact is applied to the steering wheel 2 by a secondary collision during the crash, this impact is immediately transferred to the steering column 3, so that the steering column 3 is strongly pushed in its axial direction. When an impact force exerted in the axial direction of steering column 3 exceeds a frictional force acting between the mount plate portions 7 and the stop members 9, the mount plate portions 7 slip off the bolts 10 via the cuts 8 formed in the mount plate portions 7, thus making the steering column 3 free to be displaced.
As a result, the steering column 3 is displaced ahead in the axial direction (left downward in FIG. 9) because of the impact force. With this displacement, each energy absorbing member 11 will be stretched as shown in FIG. 12. While each energy absorbing member 11 is thus stretched from the state shown in FIG. 9 to the state shown in FIG. 12, the folded portion 12 formed in the middle portion of the each energy absorbing member 11 moves from the other end side (the right side in FIG. 12) connected with the bolt 10 to one end side (the left side in FIG. 12) connected with the mount plate portion 7.
When the folded portion 12 moves in this manner, portions of the energy absorbing member 11 are plastically deformed so as to absorb the impact exerted on the steering column 3 through the steering wheel 2 by the driver's body. In the case of the depicted example, a part of the upper surface of guide plate 13 is inclined, so that the height of the guide space 14 for guiding the folded portion 12 of the each energy absorbing member 11 is gradually decreased. Because of this arrangement, in the case of the depicted example, the impact force absorbed by the energy absorbing members 11 gradually increases, thus enabling effective shock absorption.
Further, Japanese Laid-open Utility Model Application No. 4-2772 describes the shock-absorbing steering column apparatus having the structure shown in FIGS. 13 and 14. An energy absorbing member 25 is formed in the shape as shown in FIG. 14 as a plastically deformable plate, and has a base 26 and a plastically deformable belt portion 27 extending from the rear edge (the right edge in FIG. 14) of the base 26. A base end portion of this belt portion 27 extends forward and then is folded approximately 180 degrees with a sufficiently small radius of curvature to form a first folded portion 28. Further, a center portion of the belt portion 27 is folded in a U shape in a larger radius of curvature than that of the first folded portion 28 and in the opposite direction to the folded direction of the first folded portion 28 to form a second folded portion 29. Further, a connecting portion 30 is formed in a portion projecting backward further over the rear edge of the base 26 and, located at the distal end portion (the right end portion of FIG. 14) of the belt portion 27. Through holes 31, 31 are formed on either end portion of the connecting portion 30 in the transverse direction. Further, a pair of bent portions 32, 32 are formed by bending from both side edges of the base 26 toward the side where the belt portion 27 is present. Circular holes 33, 33 are formed in the free end portion (the lower edge portion of FIG. 14) of each bent portion 32, 32.
The fore end portion of the energy absorbing member 25 formed as described above is fixed to the upper surface of the outer column 17 in such a manner that the lower end portions of the pair of bent portions 32, 32 are secured to the outer side surfaces of the middle portion of the outer column 17 by bolts 34, 34 through the respective through holes 33, 33 as shown in FIG. 13. While the bent portions 32, 32 provided at one end of the energy absorbing member 25 are secured to the side surfaces of the outer column 17, the second folded portion 29 of the energy absorbing member 25 is pinched between the upper surface of the outer column 17 and the lower surface of the base 26.
The connecting portion 30 provided at the rear end of the energy absorbing member 25 is coupled with bolts 10 by inserting the bolts 10 (FIG. 9 and FIG. 12) through the through holes 31, 31 formed at the left and right end portions, so as not to be disengageable. Further, each bolt 10 passes through the cut 8 formed in the mount plate portion 7 and the through hole 15 (FIG. 12) formed in the stop member 9 mounted to each mount plate portion 7 so as to cover the cut 8, and mates with a thread hole formed in the lower surface of body 4 (FIG. 9), as described previously. The second conventional example of the shock absorbing steering column apparatus in the above structure has substantially the same operation to absorb impact energy due to secondary collision, thereby to maintain the safety of a driver's life in a crash accident as that in the first conventional example of the shock absorbing steering column apparatus described above.
Further, Japanese Laid-open Patent Application No. 3-9974 describes the shock-absorbing steering column apparatus having the structure shown in FIGS. 15 to 18. Inside the steering column 3 the steering shaft 1 having the steering wheel fixed at one end (the right end in FIG. 15) thereof is inserted so as to be rotatable. The upper support bracket 6 having the mount plate portions 7 for mounting to the body on either side is fixed by welding to the middle portion of the steering column 3. In the depicted example the steering column 3 is of the so-called collapsible type in which the outer column 17 and inner column 18 are combined in a telescopic manner.
Each energy absorbing member 37 has a base 38 as shown in FIG. 18, and a plastically deformable belt portion 39 extends from the rear edge (the right edge in FIG. 18) of this base 38. The base end portion of this belt portion 39 is folded by approximately 180 degrees with a sufficiently small radius of curvature to form a first folded portion 40. Further, the middle portion of the belt portion 39 is folded in a U shape with a larger radius of curvature than that of the first folded portion 40 and in the opposite direction to that of the first folded portion 40 to form a second folded portion 41. A connecting portion 42 is formed in the fore end portion (the right end portion in FIG. 18) of the belt portion 39 to project backward relative to the rear edge of the base 38. A through hole 43 is formed in this connecting portion 42. Upon assembling the shock absorbing steering column apparatus, a bolt 10 (FIG. 9 or FIG. 12) is inserted through the through hole 43 to secure the fore end portion of the belt portion 39 to the car body. Further, a pair of bent portions 44, 44 are formed by bending from the both side edges of the base 38 toward the side where the belt portion 39 is present.
The energy absorbing member 37 formed as described above is fixed to the lower surface of each mount plate portion 7, 7 at the front end portion thereof in such a manner that the upper edges of the pair of bent portions 44, 44 are made to abut against the lower surface of the mount plate portion 7, 7 of the upper support bracket 6 and then the abutting portions are welded. While the front end portion of the energy absorbing member 37 is fixed to the lower surface of the mount plate portion 7, 7 in this manner, the second folded portion 41 of the energy absorbing member 37 is pinched between the mount plate portion 7, 7 and the base 38.
The third conventional example of the shock absorbing steering column apparatus in the above structure functions substantially in the same manner as the first and second conventional examples of the shock absorbing steering column apparatus described above so as to absorb the impact energy due to the secondary collision in a crash to maintain the safety of a driver's life.
Incidentally, in order to effect the plastic deformation of the energy absorbing member 11, 25, 37 in a smooth manner upon secondary collision so as to efficiently absorb the impact applied on the steering column 3 during a collision, it is necessary to accurately define the distance between the two surfaces pinching the folded portion 12 or the second folded portion 29, 41 formed in the energy absorbing member 11, 25, 37, as designed. If the distance is too long (or if the two surfaces are too far from each other), the energy absorbing member 11, 25, 37 with the folded portion 12 or the second folded portion 29, 41 formed therein is plastically deformed relatively easily, resulting in insufficient absorption of impact energy. In contrast, if the distance is too short (or if the two surfaces are too close to each other), the energy necessary to plastically deform the energy absorbing member 11, 25, 37 having the folded portion 12 or the second folded portion 29, 41 formed therein becomes to great, thus resulting in insufficient absorption of impact energy as well.
In the case of the structure in the first conventional example illustrated in FIGS. 9 to 12, troublesome work is necessary to accurately define the distance between the lower surface of the mount plate portion 7 and the upper surface of the guide plate 13, as designed. Conventionally, each guide plate 13 was welded to the side surface of the upper support bracket 6, while keeping an actually assembled energy absorbing member 11 pinched between the two surfaces. This resulted in poor workability and increased the production costs of the shock absorbing steering column apparatus.
In the case of the structures in the second conventional example illustrated in FIGS. 13 and 14 and in the third conventional example shown in FIGS. 15 to 18, because the energy absorbing member 25, 37 itself forms one of the two surfaces, the assembling workability is better than that in the first conventional example. Even in the cases of these second and third conventional examples, however, the other surface needs to be provided by the member to which the energy absorbing member 25, 37 is mounted, for example in the upper support bracket 6.
It is necessary that the surfaces pinching the folded portion 28, 40 or the second folded portion 29, 41 be flat surfaces having sufficient areas. Accordingly, a flat surface needs to be provided by, for example, the upper support bracket 6. However, it might be difficult to obtain the necessary flat surface in some cases where a setting space of the upper support bracket 6 cannot be fully taken, for example in the case of the steering column apparatus for light cars.